1. Field of the Invention
The invention relates to a process for producing a high-precision metal reflector and to a metal reflector. A projection system also forms the subject matter of the invention.
2. Description of Related Art
In practice, reflectors have a wide range of applications; mention may be made in particular of headlamp reflectors, in particular in the automotive industry, and of reflectors as used for projection systems, for example digital projectors.
DE 100 29 905 describes a reflector for a motor vehicle, in which a cold-light coating has been applied by means of a deposition process. The reflector has a base body made from plastic.
Plastic reflectors of this type have the drawback of not being particularly heat-resistant. In particular if the reflector is provided with what is known as a cold-light mirror coating, i.e. a layer which transmits and partially absorbs infrared radiation, high thermal stresses are produced in particular in the case of high-power projection systems.
Deep-drawn metal reflectors, which are likewise often used in practice, often do not have the required accuracy. Furthermore, these reflectors are relatively thin. On account of this small volume of material, it is difficult to sufficiently dissipate the heat, in particular in a projection system, and consequently the reflector reaches very high temperatures.
U.S. Pat. No. 3,944,320 discloses a cold-light mirror with an enameled coating. A particular drawback of enameled coatings of this type is that it is impossible to achieve a very high level of accuracy, which has an adverse effect on the optical quality of a projection system. Furthermore, the enamel layer is highly temperature-sensitive, and consequently a mirror of this type cannot be used for high-power projectors.
To achieve good optical properties, reflectors with a base body made from glass are primarily used for high-power projectors. Reflectors of this type are distinguished by a relatively high accuracy. However, one drawback is that glass is a relatively poor conductor of heat, and consequently it is difficult to dissipate the heat in particular in high-power projectors, which leads to high temperatures, in particular at the reflector surface. This applies in particular if the reflector has a cold-light mirror coating, i.e. a layer which preferably transmits infrared radiation and is reflective in at least a partial region of the visible spectrum. Since a certain proportion of the infrared radiation which passes through the glass body is absorbed by the latter, the glass body is considerably heated. Therefore, glass reflectors in high-power projection systems usually have only a limited service life.